Tendon‐derived extracellular matrix induces mesenchymal stem cell tenogenesis via an integrin/transforming growth factor‐β crosstalk‐mediated mechanism

Treatment of tendon injuries is challenging. To develop means to augment tendon regeneration, we have previously prepared a soluble, low immunogenic (DNA-free), tendon extracellular matrix fraction (tECM) by urea extraction of juvenile bovine tendons, which is capable of enhancing transforming growth factor-beta (TGF-beta) mediated tenogenesis in human adipose-derived stem cells (hASCs). Here, we aimed to elucidate the mechanism of tECM-driven hASC tenogenic differentiation in vitro, focusing on the integrin and TGF-beta/SMAD pathways. Our results showed that tECM promoted hASC proliferation and tenogenic differentiation in vitro based on tenogenesis-associated markers. tECM also induced higher expression of several integrin subunits and TGF-beta receptors, and nuclear translocation of p-SMAD2 in hASCs. Pharmacological inhibition of integrin-ECM binding, focal adhesion kinase (FAK) signaling, or TGF-beta signaling independently led to compromised pro-tenogenic effects of tECM and actin fiber polymerization. Additionally, integrin blockade inhibited tECM-driven TGFBR2 expression, while inhibiting TGF-beta signaling decreased tECM-mediated expression of integrin alpha1, alpha2, and beta1 in hASCs. Together, these findings suggest that the strong pro-tenogenic bioactivity of tECM is regulated via integrin/TGF-beta signaling crosstalk. Understanding how integrins interact with signaling by TGF-beta and/or other growth factors (GFs) within the tendon ECM microenvironment will provide a rational basis for an ECM-based approach for tendon repair.